Printing apparatus of the general type with which the present invention is concerned are known. They operate with a supply of tape arranged to receive an image and a means for transferring the image onto the tape. In one known device, there is a tape holding case which holds a supply of image receiving tape and a supply of an image transfer ribbon, the image receiving tape and the transfer ribbon being passed in overlap through a printing zone of the printing device. At the print zone, a thermal print head cooperates with a platen to transfer an image from the transfer ribbon to the tape. A printing device operating with a tape holding case of this type is described for example in EP-A-0267890 (Varitronics, Inc.). Other printing devices have been made in which letters are transferred to an image receiving tape by a dry lettering or dry film impression process. In all of these printing devices, the construction of the image receiving tape is substantially the same. That is, it comprises an upper layer for receiving an image which is secured to a releasable backing layer by a layer of adhesive.
The upper layer can either receive an image on its top surface, its lower surface being secured to the releaseable backing layer by a layer of adhesive or alternatively the upper layer can be transparent and can receive an image on one of its faces printed as a mirror image so that it is viewed the correct way round through the other surface of the tape. In this case, a double sided adhesive layer can be secured to the upper layer, this double sided adhesive layer having a releaseable backing layer. This latter arrangement is described for example in EP-A-0322918 (Brother Kogyo Kabushiki Kaisha).
In another type of printing device (described for example in our European Application No. EP-A-0573187, there are two separate tape holding cases, one holding image receiving tape and the other holding an image transfer ribbon.
With all such printing devices it is desirable that they are able to operate with image receiving tapes of different widths. For this, the apparatus should include a way of identifying the width of tape within the tape holding case so that printing can be correctly carried out or inhibited where an incorrect tape is inserted. For example if tape of a narrower width is used, printing should be confined to the area of the narrow width tape and should not extend to a width suitable for a wider tape.
There have been various proposals made to identify the width of tape within a tape holding case. In U.S. Pat. No. 5,078,523 (Varitronics, Inc.), an electrical sensing arrangement is used responsive to different resistive values. Each tape holding case holds a tape of a predetermined width and has a resistor of a predetermined resistive value associated with that width. On insertion of the tape holding case into the printing apparatus, the resistive value is sensed and the width of tape within the tape holding case is thereby identified.
In EP-A-0497352 (Casio), tape holding cases having tapes of different widths are arranged to actuate different micro-switches when inserted into the printing device. Thus, the width of tape is identified by a variation in the external casing of the tape holding case.
In EP-A-0526078 (Brother), the shape of a tape holding case interacts with an optical sensor to identify the width of tape therein.
The present invention seeks to provide a different solution to the problem of identification of different tape widths within a tape holding case, which is cheaper and simpler than the above mentioned solutions and which enables a user to positively set the tape width which he requires.